This disclosure relates generally to video surveillance systems and, more particularly, to reducing oscillations in video images and audible noise from video camera assemblies which contain motors.
At least some known video surveillance systems include one or more video camera assemblies that typically include a video camera mounted in a housing along with a pan, tilt, and zoom (PTZ) assembly. The PTZ permits controlling a movement of the camera to align a viewing area of the camera with an object of interest or location of interest. The zoom portion of the mechanism may be used to adjust a field of view of the camera. The housing protects the camera from the environment in the location where the camera and PTZ assembly are mounted.
Video camera assemblies such as security cameras are installed in various manners. The PTZ assemblies generally include a motor for positioning the video camera about an axis of rotation and an angular position encoder for determining the position of the camera along the respective axis of rotation. In video camera assemblies that use closed loop position control, the encoder output is used to determine whether the camera is pointed at the commanded angle. If not, a motor drive signal is transmitted to the motor to drive the camera to the commended position. In some known video camera assemblies, the angular resolution of the encoder is greater than the angular resolution of the motor. In such assemblies, it is possible that the camera may be commanded to a position that is between positions that the motor can maintain in steady state. In such an instance, the motor may oscillate between two positions in an attempt to position the camera to the commanded angle. Such oscillation causes the motor windings to vibrate such that an undesirable audible noise is generated.